Fix how fail_with() is used

fail_with() is a function in lib/msf/core/exploit.rb, which indicates that this is meant to be used only for exploit modules. Because of that, it should NOT be seen in places like mixins or auxiliary modules, otherwise you will get a "NoMethodError undefined method `fail_with'" error - [See RM 8265] for example.

Instead of using fail_with(), the closest replacement for that is to fall back to raise Runtime, which is also something we used a lot before fail_with was created.